1. The Field of the Invention
The present invention relates generally to mounting systems for positioning and securing a component on a shaft. More particularly, embodiments of the present invention relate to target anode mounting systems and devices that include various features which serve to reliably and effectively establish and maintain the both the axial and radial position of the target anode in a variety of operating conditions.
2. Related Technology
X-ray producing devices are valuable tools that are used in a wide variety of industrial, medical, and other applications. For example, such equipment is commonly used in areas such as diagnostic and therapeutic radiology, semiconductor manufacture and fabrication, and materials analysis and testing. While they are used in various different applications, the different x-ray devices share the same underlying operational principles. In general, x-rays, or x-ray radiation, are produced when electrons are produced, accelerated, and then impinged upon a material of a particular composition.
Typically, these processes are carried out within a vacuum enclosure. Disposed within the vacuum enclosure is an electron generator, or cathode, and a target anode, which is spaced apart from the cathode. In operation, electrical power is applied to a filament portion of the cathode, which causes a stream of electrons to be emitted by the process of thermionic emission. A high voltage potential applied across the anode and the cathode causes the electrons emitted from the cathode to rapidly accelerate towards a target surface, or focal track, positioned on the target anode.
The accelerating electrons in the stream strike the target surface, typically a refractory metal having a high atomic number, at a high velocity and a portion of the kinetic energy of the striking electron stream is converted to electromagnetic waves of very high frequency, or x-rays. The resulting x-rays emanate from the target surface, and are then collimated through a window formed in the x-ray tube for penetration into an object, such as the body of a patient. As is well known, the x-rays can be used for therapeutic treatment, or for x-ray medical diagnostic examination or material analysis procedures.
Due to the nature of the operation of an x-ray tube, components of the x-ray tube are subjected to a variety of demanding operating conditions. For example, in addition to stimulating the production of x-rays, the kinetic energy of the striking electron stream also causes a significant amount of heat to be produced in the target anode. As a result, the target anode typically experiences extremely high operating temperatures, as high as 2300° C. during normal operations. However, the anode is not the only element of the x-ray tube subjected to such operating temperatures. For example, components such as the shaft, and the nut which secures the target anode on the shaft, are also exposed to these high temperatures as a result of their proximity to, and substantial contact with, the target anode.
In addition to experiencing high operating temperatures, the components of the x-ray device are also exposed to thermal stress cycling situations where relatively wide variations in operating temperature may occur in a relatively short period of time. By way of example, the temperature in the region of the target anode may, in some cases, increase from about 20° C. to about 1250° C. in a matter of minutes. The relatively rapid rate at which such temperature changes take place imposes high levels of thermally-induced stress and strain in the x-ray tube components.
Further, many of the rotating components of a typical rotating anode type x-ray device are additionally subjected to high levels of non-thermally induced mechanical stress induced by high speed rotation of the anode and shaft. For example, in many rotating anode type x-ray devices, the anode, the shaft and the nut used to attach the anode to the shaft, are subjected to high stress “boost and brake” cycles. In a typical boost and brake cycle, the anode may be accelerated from zero to ten thousand (10,000) revolutions per minute (RPM) in less than ten seconds. This high rate of acceleration imposes significant mechanical stresses on the anode, the shaft and the nut. Thus, the components which are used to secure the anode in position are exposed not only to extreme thermal stresses, but are simultaneously exposed to significant stresses imposed by the mechanical operations of the x-ray device.
The operating conditions just described have a variety of effects that may be detrimental to the operation and service life of the x-ray tube. At least some of such effects concern the attachment of the target anode to the shaft.
For example, it may be desirable in some instances to define a gap between the outside diameter of the shaft and the opening in the anode through which the shaft passes. Such a gap would permit manipulation of anode orientation prior to operation of the x-ray device. In particular, the gap allows the assembler to attempt to minimize anode run-out with respect to the shaft by shifting the lateral, or radial, position of the anode slightly prior to tightening the nut. However, while such a gap may be useful in the sense that it permits initial positioning of the anode with respect to the shaft, the gap also allows the possibility of undesirable lateral movement, or radial runout, of the anode when the anode is subjected to mechanical and thermal stresses.
Failure to compensate for, or otherwise eliminate, such radial runout by limiting or preventing the movement of the target anode may cause problems with the operation of the device. For example, high operational speeds and mechanical stresses may cause a target anode that is relatively unconstrained from radial movement to vibrate and produce noise during operation of the x-ray device. Vibration may also result when the target anode is not centered with respect to the rotor shaft. Such vibration and noise, in turn, have various negative consequences with respect to the performance and operational life of the x-ray device.
For example, vibration and/or movement of the target anode will cause corresponding movement of the focal spot on the target surface of the anode. Because high quality imaging depends upon reliable maintenance of focal spot positioning, any such focal spot movement will compromise the quality of the images that can be produced with the x-ray device. Furthermore, unchecked vibration may ultimately damage the target anode, shaft, the nut, or other components of the x-ray device. Moreover, noise and vibration may be unsettling to the x-ray device operator and the x-ray subject, particularly in mammographic applications where the subject is in relatively intimate contact with the x-ray device.
In view of the foregoing problems, and others, a need exists for a component mounting system that substantially prevents radial runout of the mounted component and thereby substantially reduces the noise, vibration, and other effects associated with unbalanced and inadequately unconstrained components.